US5046040A - Microprogram control apparatus using don't care bits as part of address bits for common instructions and generating variable control bits - Google Patents

Microprogram control apparatus using don't care bits as part of address bits for common instructions and generating variable control bits Download PDF

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Publication number
US5046040A
US5046040A US07/947,642 US94764286A US5046040A US 5046040 A US5046040 A US 5046040A US 94764286 A US94764286 A US 94764286A US 5046040 A US5046040 A US 5046040A
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microcode
address
decoding
microcodes
counter
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US5310049A (en
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Akio Miyoshi
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Toshiba Corp
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Toshiba Corp
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    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F9/00—Arrangements for program control, e.g. control units
    • G06F9/06—Arrangements for program control, e.g. control units using stored programs, i.e. using an internal store of processing equipment to receive or retain programs
    • G06F9/30—Arrangements for executing machine instructions, e.g. instruction decode
    • G06F9/30145—Instruction analysis, e.g. decoding, instruction word fields
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F9/00—Arrangements for program control, e.g. control units
    • G06F9/06—Arrangements for program control, e.g. control units using stored programs, i.e. using an internal store of processing equipment to receive or retain programs
    • G06F9/22—Microcontrol or microprogram arrangements
    • G06F9/223—Execution means for microinstructions irrespective of the microinstruction function, e.g. decoding of microinstructions and nanoinstructions; timing of microinstructions; programmable logic arrays; delays and fan-out problems
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F9/00—Arrangements for program control, e.g. control units
    • G06F9/06—Arrangements for program control, e.g. control units using stored programs, i.e. using an internal store of processing equipment to receive or retain programs
    • G06F9/22—Microcontrol or microprogram arrangements
    • G06F9/26—Address formation of the next micro-instruction ; Microprogram storage or retrieval arrangements
    • G06F9/262—Arrangements for next microinstruction selection
    • G06F9/268—Microinstruction selection not based on processing results, e.g. interrupt, patch, first cycle store, diagnostic programs

Definitions

  • the present invention relates generally to a microprogram control device, and more particularly, to a microprogram control device used in a computer, for example, a microcomputer or microprocessor.
  • FIG. 5 An example of a conventional microprogram control device is shown in FIG. 5.
  • a machine instruction code from a program memory (not shown) or the like is directly input to an address register 101.
  • This address register 101 produces an output of 8 bits, which are high-order bits of a microcode address.
  • a counter 102 reset in synchronism with the fetch of the machine instruction code sent to the register 101, produces an output of 4 bits, which are low-order bits of the microcode address.
  • microcode address decoding area 103a which is part of a microcode storage unit 103, and can be in the form of, for example, a PLA (programmable logic array).
  • the address decoding area 103a of microcode storage unit 103 decodes the input microcode address, causing a microcode stored in the addressed segment of a microcode memory area 103b to be output to a microinstruction register 104.
  • the contents of the counter 102 are incremented without altering the contents of the address register 101, thus causing sequential microcode addresses to be designated.
  • the conventional microcode storage unit 103 is configured as shown in FIG. 6.
  • the address decoding area 103a has a series of microcode addresses. Each microcode address has, for example, 12 bits. Associated with each microcode address is a microcode of; for example, 21 bits, which microcode is stored within the microcode memory area 103b.
  • the microprogram having three microcodes of "aa . . . a", “bb . . . b", and “cc . . . c” is stored.
  • the microprogram having two microcodes of "dd . . . d” and "ee . . . e” is stored.
  • the microprogram having three microcodes of "aa . . . a", bb . . . b", and "cc . . . c" identical to the three microcodes of the INC instruction is stored.
  • the microprogram having three microcodes of "xx . . . x", "yy . . . y”, and "zz . . . z" is stored. Note that areas represented by "** . . . *" are unnecessary memory areas since no microcodes for the given machine instruction microprogram need to be stored in these unused memory areas.
  • the above-mentioned conventional microprogram control device is required to produce a microprogram for each machine instruction.
  • counter 102 is used to create the low-order bits of the microcode address.
  • Counter 102 is reset for each fetch of a machine instruction being called.
  • microcodes corresponding to each instruction are accessed in sequence from the start address of the microprogram being outputted.
  • the microstep is fixed to a preselected number of steps, for example, four steps.
  • FIG. 7 Another example of a conventional microprogram control device will be described with reference to FIG. 7.
  • a machine instruction is decoded by machine instruction decoding circuit 110.
  • Circuit 110 is typically comprised of PLA, such that microinstruction addresses from circuit 110 are input to a next microinstruction address determination circuit ill.
  • a next microinstruction address output by circuit 111 is input to a control memory or store 112 and to an address converter 114.
  • Control memory 112 then outputs a microinstruction address to a microinstruction register 113.
  • This microinstruction register 113 comprises a conditional branch instruction 113b, and another instruction 113a.
  • a control memory address (that is, the next microinstruction address of the concerned microinstruction) is first converted into a nanoinstruction address by address converter 114.
  • the nanoinstruction is then stored in nanoinstruction register 115.
  • Microinstruction 113a has an NMA (next microinstruction address) field that represents an address of the next microinstruction.
  • NMA next microinstruction address
  • the NMA field is output to the microinstruction address bus 120.
  • the TY field represents a value other than "00”
  • the microinstruction address is determined by the output of the machine instruction decoding circuit 110.
  • status information of 2 bits selected by a CBC field is coupled to a NMAB (next microinstruction address branch) field by status selection circuit 119.
  • a nanoinstruction of an address stored in nanoinstruction address register 115 is output from nanomemory 116, which nanoinstruction is then stored in nanoinstruction register 117.
  • Computing unit 118 performs predetermined computations in accordance with this nanoinstruction.
  • Status information for example, at carry flag, etc., produced by this computation is input to the status selection circuit 119.
  • Status selection circuit 119 selects the status information from the computing unit 118 based on the content of the CBC field of the microinstruction 113b, and then outputs to the next microinstruction address determination circuit 111.
  • an object of the current invention is to provide a microprogram control device which improves operating speed and decreases semiconductor chip area.
  • Another object of the present invention is to realize a microprogram control device that has both a variable microstep function and simplified circuit construction.
  • a microprogram control device adapted for use with a microcomputer which comprises: a decoding circuit for decoding machine instruction codes input from a program memory to the decoding circuit to create microcode start addresses for each of said machine instruction codes; a counter connected to said decoding circuit operative to count in response to the receipt of each of the microcode start addresses to produce a required number of microcode addresses; and a microcode storage unit connected to the counter comprising an address decoding area responsive to the receipt of each of said microcode addresses from the counter to produce microcodes corresponding to the microcode addresses, and a microcode memory area in which the microcodes of the microprograms defining the machine instruction codes are stored whereby when each microcode start address is input from the decoding circuit to the counter.
  • the address decoding area sequentially designates microcodes in accordance with each microcode start address and provides an access to the microcode memory area.
  • a predetermined microcode is read on the basis of the microcode designation of the address decoding area, and is provided for controlling circuit means.
  • the microprogram control device of the present invention provides a "don't care" function for a certain bit or bits of common microcode addresses of the common microcodes with a view to realizing access of the common microcodes by the different machine instructions.
  • a "don't care" function for a certain bit or bits of common microcode addresses of the common microcodes with a view to realizing access of the common microcodes by the different machine instructions.
  • a next microinstruction address determination circuit is disposed between the machine instruction decoder and the counter.
  • the determination circuit selects either a microcode start address from the machine instruction decoder or a microcode start address of the next microinstruction contained in the microcode output from the register, depending upon a control bit(s) in the microcodes provided to the counter. In this manner, the determination circuit enables designation of a branch operation as a microcode to generate various kinds of machine instructions.
  • the counter may be provided with an area of a high-order bit assigned to a register and a remaining area assigned to the counter itself.
  • FIG. 1 is a block diagram illustrating an embodiment of a microprogram control device according to the present invention
  • FIG. 2 is a schematic view diagrammatically showing the operation of the device of the present invention shown in FIG. 1;
  • FIG. 3A to 3C are explanatory views showing microcode storage conditions when microcode defining different machine instructions are partially common to each other, wherein FIGS. 3A and 3B are examples with conventional microprogram control devices, and FIG. 3C is an example with a microprogram control device according to the present invention;
  • FIG. 4 is a block diagram illustrating another embodiment of a microprogram control device according to the present invention.
  • FIG. 5 is a block diagram illustrating a conventional microprogram control device
  • FIG. 6 is a explanatory view diagrammatically showing the operation of the conventional device shown in FIG. 5;
  • FIG. 7 is at block diagram illustrating another conventional microprogram control device.
  • FIG. 1 there is shown in a block form an embodiment of a microprogram control device according to the present invention.
  • the microprogram control device of this embodiment comprises a machine instruction decoder 11, preferably in the form of a PLA or read only memory (ROM), that sequentially decodes machine instructions of, for example, 8 bits that are fetched from external memory (not shown) of a computer (not shown).
  • a machine instruction decoder 11 preferably in the form of a PLA or read only memory (ROM)
  • Microcode start addresses of 10 bits per each machine instruction are generated, and a counter 12 counts up to generate the required number of microcode addresses. Incremental operation of counter 12 is synchronized by clock signal CLK.
  • a control signal or control bit(s) Sc (to be referred to later) is input to counter 12 at this point for rendering variable microstep functions in the microprogram control device.
  • the microprogram control device further includes a microcode storage unit 13 of two areas 13a and 13b and is made up of, for example, PLA or ROM.
  • Decoding area 13a of microcode storage unit 13 responds to microcode addresses from counter 12, and generates microcode addresses.
  • Memory area 13b of microcode storage unit 33 stores the plurality of microcodes defining machine instructions in accordance with respective start addresses. When each start address is input from counter 12 to address decoding area 13a, address decoding area 13a sequentially designates to memory area 13b a microcode address per each microstep, thus predetermined microcodes of n bits are stored in microcode memory area 13b based on the address provided by address decoding area 13a.
  • microcode read from microcode memory area 13b is output to a microcode register 14.
  • Microcodes latched in the microcode register 14 are output in order to control the operation of subsequent circuits to be controlled 25.
  • Part of the output microcode from the microcode register 14 becomes control output bit(s) Sc, and is input back to counter 12.
  • the control output Sc controls the counter 12.
  • counter 12 either counts up to create microcode addresses per each machine instruction, or shifts to loading the next machine instruction depending upon the logic state of the control signal Sc.
  • Machine instruction decoding circuit 11 and the microcode storage unit 13 will now be described in detail with reference to FIG. 2.
  • Machine instruction decoding circuit 11 is a matrix circuit that decodes machine instruction codes and creates start addresses of microcodes correspondingly stored in microcode storage unit 13. Decoding circuit 11 effects said decoding operation in connection with the example shown in FIG. 2 as follows.
  • a start address "0000000000” is read.
  • a start address "0000000011” is read.
  • a start address "00001101” of the SHIFT instruction a start address "0000000000” is read.
  • a start address "0000000101” is read.
  • microcode memory area 13b of microcodes storage unit 13 a plurality of microcodes are stored in correspondence with respective microcode addresses designated by the address decoding area 13a. Namely, a microcode represented by "aa . . . a” is stored at address 0000000000, a microcode represented by "bb . . . b” is stored at address 0000000001, a microcode represented by “cc . . . c” is stored at address 0000000010, a microcode represented by "dd . . . d” is stored at address 0000000011, a microcode represented by "ee . . . e” is stored at address 0000000100, a microcode represented by "xx . . . x" is stored at address 0000000101, a microcode represented by "yy . . . y” is stored at address 0000000110, and a microcode represented by "zz . . . z is stored at address 0000000111.
  • the address "0000000000” is input to microcode storage unit 13, and microcode represented by "aa . . . a” is output. Subsequently, when counter 12 counts up in synchronism with the clock signal CLK, the microcode of "bb . . . b” corresponding to the next address "00000000011", is output. Likewise, when the counter 12 further counts up, the microcode of "cc . . . c" corresponding to the next address "0000000010" is output. Thus, a microprogram having an output of three steps in respect to the INC instruction is generated.
  • the address "0000000011” is input to microcode storage unit 13, and microcode represented by “dd . . . d” is output. Subsequently, when counter 12 counts up by one in synchronism with clock signal CLE, the microcode "ee . . . e” corresponding to the next address "0000000100” is output. Thus, a microprogram having an output of two steps in respect of the MOV instruction is generated.
  • the SHIFT instruction is generated identically to the INC instruction. Accordingly, when the SHIFT instruction is input to the machine instruction decoding Circuit 11, the same address "0000000000" as the INC instruction is input to microcode storage unit 13. As previously described, a microprogram output having three steps represented by "aa . . . a", "bb . . . b” and "cc . . . c" is sequentially generated.
  • microcode storage unit 13 When the ADD instruction is input to the machine instruction decoding circuit ii, the address "00000000101" is input to microcode storage unit 13, and microcode represented by "xx . . . x" is output. Subsequently, when the counter 12 counts up by one in synchronism with the clock signal CLK, the microcode “yy . . . y” corresponding to the next address "000000011011” is output. When counter 12 further counts up by one in synchronism with the clock signal CLK, microcode "zz . . . z” corresponding to the next address "0000000111" is output. Thus, a microprogram output having three steps in respect to the ADD instruction is generated.
  • microcodes defining the machine instruction are partially common to each other, the present invention makes possible the generation of microprograms with less memory capacity requirements than conventional devices, and without reducing operating speed, by configuring microcode storage unit 13 in a manner now described.
  • machine instruction INSTR1 has a microprogram having eight microcode steps shown as "aa . . . a”, "bb . . . b", “cc . . . c", “dd . . . d”, "ee . . . e”, “ff . . . f", “gg . . . g” and "hh . . . h", respectively
  • machine instruction INSTR2 has a microprogram having eight microcode steps shown as "xx . . .
  • this embodiment according to the present invention can provide a function of "don't care" for a certain number of addresses for microcodes common to microprograms of successive machine instructions INSTR1 and INSTR2.
  • the present invention permits microprogramming to be done with reduced memory capacity and without lowering operating speed of the microcomputer.
  • the microcode "aa . . . a" of the microprogram is stored at an address 0010010000
  • the microcode "bb . . . b” is stored at an address 001001000
  • the microcode "cc . . . c” is stored at an address 0010010010.
  • the microcode "xx . . . x" of the microprogram is stored at address 0010011000
  • microcode "yy . . . y” is stored at address 0010011001
  • microcode "zz . . . z" is stored at address 0010011010.
  • microcodes of the two microprograms are stored in microcode storage unit 13, with the fourth bit from the lowest or rightmost bit of each address for the common microcodes being a "don't care" bit, which can be arbitrarily defined in its logical state.
  • microcode "dd . . . d” is stored at an address 001001x011 (x represents a bit which undergoes the "don't care” operation), the microcode "ee . . . e” at an address 001001x100, microcode "ff . . . f” at an address 001001x101, microcode "gg . . . g” at an address 001001x110, and microcode "hh . . . h” at an address 001001x111.
  • this embodiment of the present invention operates with microcodes, thus making it possible to reduce memory requirements of the microcode storage unit 13. Further, since branch operations, for example, jumps, etc., are not needed, execution time of the microcomputer remains constant. In addition, unlike conventional devices, the present invention does not require control memory for the next address of the microprogram.
  • next microinstruction address determination circuit 15 is a multiplexer to select either a start address of the microinstruction address from machine instruction decoder 11 or signal Ad (i.e., or a start address of the next microinstruction contained in the microcode), depending upon control signal Br from microcode decoding circuit 20.
  • Control signal Br is output from microcode decoding circuit 20.
  • Control signal Sc also output from microcode decoding circuit 20, is input to counter 12.
  • the control signals Br and Sc are provided by decoding microcode signals, computing unit status signals and timing control signals which include the machine instruction fetch status.
  • the control signal Sc is used to set the counter with the value from next microinstruction address determination circuit when a new machine instruction is started or a jump microinstruction is executed.
  • this embodiment designates branch operations used to generate microprograms of various kinds of machine instructions.
  • the present invention can easily be modified to perform similar functions without being limited to the above-mentioned embodiments.
  • the counter may be provided with an area of high-order bits assigned to a register and a remaining area assigned to the counter itself.
  • a plurality of "don't care" bits are provided, it is possible to cope with microcode common to the microprograms of three or more machine instructions.

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US07/947,642 1986-01-16 1986-12-30 Microprogram control apparatus using don't care bits as part of address bits for common instructions and generating variable control bits Expired - Fee Related US5046040A (en)

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US5313600A (en) * 1988-12-02 1994-05-17 Mitsubishi Denki Kabushiki Kaisha System for controlling the number of data pieces in a queue memory
US5333287A (en) * 1988-12-21 1994-07-26 International Business Machines Corporation System for executing microinstruction routines by using hardware to calculate initialization parameters required therefore based upon processor status and control parameters
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US5452428A (en) * 1988-01-18 1995-09-19 Kabushiki Kaisha Toshiba Processor having different operand source information temporarily stored in plural holding registers to avoid using microprogram ROM capacity for such information
US5500930A (en) * 1988-11-04 1996-03-19 Fujitsu Limited System to decode instructions indicating the addresses of control codes and providing patterns to direct an electron beam exposure apparatus
US5636374A (en) * 1994-01-04 1997-06-03 Intel Corporation Method and apparatus for performing operations based upon the addresses of microinstructions
US5651122A (en) * 1991-05-13 1997-07-22 Motorola, Inc. Pipelined data processor that detects an illegal instruction by detecting legal instruction operation codes
US5958046A (en) * 1996-11-26 1999-09-28 Texas Instruments Incorporated Microprocessor with reduced microcode space requirements due to improved branch target microaddress circuits, systems, and methods
US5983344A (en) * 1997-03-19 1999-11-09 Integrated Device Technology, Inc. Combining ALU and memory storage micro instructions by using an address latch to maintain an address calculated by a first micro instruction
US20010008017A1 (en) * 1998-08-03 2001-07-12 Moore William P. Microprocessor including controller for reduced power consumption and method therefor
WO2003029960A1 (en) * 2001-10-01 2003-04-10 Benjamin Cooper General purpose fixed instruction set (fis) bit-slice feedback processor unit/computer system
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US5636374A (en) * 1994-01-04 1997-06-03 Intel Corporation Method and apparatus for performing operations based upon the addresses of microinstructions
US5958046A (en) * 1996-11-26 1999-09-28 Texas Instruments Incorporated Microprocessor with reduced microcode space requirements due to improved branch target microaddress circuits, systems, and methods
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